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En vue de l'obtention du
DOCTORAT DE L'UNIVERSITÉ DE TOULOUSEDélivré par :
Institut National Polytechnique de Toulouse (INP Toulouse)Discipline ou spécialité :
Réseaux, Télécommunications, Systèmes et Architecture
Présentée et soutenue par :Mme BOUCHRA BENAMMARle vendredi 5 décembre 2014
Titre :
Unité de recherche :
Ecole doctorale :
FORMES D'ONDES AVANCEES ET TRAITEMENTS ITERATIFS POURLES CANAUX NON LINEAIRES SATELLITES
Mathématiques, Informatique, Télécommunications de Toulouse (MITT)
Institut de Recherche en Informatique de Toulouse (I.R.I.T.)Directeur(s) de Thèse :
MME MARIE LAURE BOUCHERETMME NATHALIE THOMAS
Rapporteurs :M. CHRISTOPHE LAOT, TELECOM BRETAGNE CAMPUS DE BREST
M. PIERRE DUHAMEL, SUPELEC
Membre(s) du jury :1 M. PHILIPPE CIBLAT, TELECOM PARISTECH, Président2 M. CHARLY POULLIAT, INP TOULOUSE, Membre2 M. MARCO LOPS, UNIVERSITA DEGLI STUDI DI CASSINO, Membre2 M. MATHIEU DERVIN, THALES ALENIA SPACE, Membre2 Mme MARIE LAURE BOUCHERET, INP TOULOUSE, Membre2 Mme NATHALIE THOMAS, INP TOULOUSE, Membre
ii
Remerciements
Je tiens tout d'abord à remercier mes encadrants de thèse pour m'avoir fait con�ance, et soutenu du-
rant ma thèse. Plus spécialement, je remercie Marie-Laure Boucheret pour ses éclairages salutaires au
sujet des modulations en mono et multi-porteuse, et que personne ne s'avise de dire que le SC-FDMA
est une modulation mutli-porteuse au risque de s'attirer les foudres de Marie-Laure. Je remercie aussi
Nathalie Thomas, pour ses nombreuses relectures et pour sa gentillesse en toute circonstance qui ont
eu un e�et ô combien réconfortant (merci pour les bonbons). Mes remerciements vont aussi à Charly
Poulliat pour m'avoir guidé tout au long de ma thèse et avoir été présent à toute heure a�n de me
relire, qu'il trouve en mes mots toute ma gratitude.
Durant ces trois années de thèse, j'ai aussi eu des échanges avec Mathieu Dervin ingénieur de
recherche à Thalès. Je souhaiterai le remercier pour sa disponibilité. Il a sû répondre de manière très
pédagogique à mes innombrables questions aux sujets des enjeux des systèmes actuels.
Je remercie aussi Pierre Duhamel Directeur de recherche CNRS au sein du Laboratoire Signaux
et Systèmes de Paris ainsi que Christophe Laot Professeur à TELECOM Bretagne qui m'ont fait
l'honneur de rapporter ma thèse. Que soient aussi remerciés Philippe Ciblat professeur à TELECOM
ParisTech et Marco Lops professeur à l'université de Cassino en Italie pour avoir accepté d'examiner
ma thèse.
Ensuite, parce que la vie du laboratoire n'aurait pas été aussi agréable sans eux, je souhaite
remercier de tout coeur tous mes amis et collègues de laboratoire. Plus spécialement je remercie,
Abdé, Cécilé, Yoann, Qi, Ningning, Sébastien, Olivier (dit Jack-Sparrow), Sokchenda (agent SS),
Romain, Bilel, Farouk, Ahmad, Mohammad, Mohamed, Aziz, Nesrine, JB (the hat man), Farouk,
iii
Facundo, Emilie, Jean-Gabriel (dit le corse) et Hermine. N'oublions pas les TeSA-people (les gens de
l'au-delà ... du canal) Raoul, Victor, Jorge (dit Georges), Jean-Adrien (l'acteur), Tarik (le penseur)
et Fabio. Comment oublier ces parties de Hanabi, de contact, de bowling ou de speed-cubing ? Que
cela soit sur le terrain de foot, perchés au sommet du Montségur, en pique-nique à Pech David ou
mieux encore, a�alés sur la piste de la patinoire, vous avez su rendre inoubliable mon séjour parmi
vous. Je vous souhaite à tous tout le bonheur et la réussite que l'on peut espérer.
Mes derniers remerciements vont à ceux sans qui rien de tout cela n'aurait été possible. Je remercie
très chaleureusement mes parents pour leur sacri�ces a�n de me permettre de venir étudier en France,
mon frère et en�n ma moitié pour m'avoir soutenue durant ma thèse et avoir partagé mes joies et
mes peines. Je souhaite que vous trouviez dans mes mots l'expression de mon sincère respect et amour.
Bouchra
iv
Résumé
L'augmentation de l'e�cacité spectrale des transmissions mono-porteuses sur un lien de di�usion par
satellite est devenu un dé� d'envergure a�n de pallier la demande croissante en débits de transmission.
Si des techniques émergentes de transmissions encouragent l'utilisation de modulations à ordre élevé
telles que les modulations de phase et d'amplitude (APSK), certaines dégradations sont encourues lors
du traitement à bord du satellite. En e�et, en raison de l'utilisation d'ampli�cateurs de puissance ainsi
que de �ltres à mémoires, les modulations d'ordre élevé subissent des distorsions non-linéaires dues à la
�uctuation de leur enveloppe, ce qui nécessite des traitements au sein de l'émetteur ou bien au sein du
récepteur. Dans cette thèse, nous nous intéressons au traitement de l'interférence non-linéaire au sein
du récepteur, avec une attention particulière aux égaliseurs itératifs qui améliorent les performances du
système au prix d'une complexité élevée. A partir du modèle temporel des interférences non-linéaires
induites par l'ampli�cateur de puissance, des algorithmes de réception optimaux et sous optimaux
sont dérivés, et leurs performances comparées. Des égaliseurs à complexité réduite sont aussi étudiés
dans le but d'atteindre un compromis performances-complexité satisfaisant. Ensuite, un modèle des
non-linéarités est dérivé dans le domaine fréquentiel, et les égaliseurs correspondants sont présentés.
Dans un second temps, nous analysons et dérivons des récepteurs itératifs pour l'interférence entre
symboles non linéaire. L'objectif est d'optimiser les polynômes de distributions d'un code externe
basé sur les codes de contrôle de parité à faible densité (LDPC) a�n de coller au mieux à la sortie
de l'égaliseur. Le récepteur ainsi optimisé atteint de meilleures performances comparé à un récepteur
non optimisé pour le canal non-linéaire. Finalement, nous nous intéressons à une classe spéci�que
de techniques de transmissions mono-porteuse basée sur le multiplexage par division de fréquence
v
(SC-OFDM) pour les liens satellites. L'avantage de ces formes d'ondes réside dans l'e�cacité de leur
égaliseur dans le domaine fréquentiel. Des formules analytiques de la densité spectrale de puissance
et du rapport signal sur bruit et interférence sont dérivées et utilisées a�n de prédire les performances
du système.
Publications
Journals in preparation
1. B.Benammar, N.Thomas, C.Poulliat, ML.Boucheret, M.Dervin, "Iterative Receivers For Non Linear
Satellite Channels" to be submitted to IEEE trans. on Communications.
2. B.Benammar, N.Thomas, C.Poulliat, ML.Boucheret, M.Dervin, "Performance Analysis Of Block Circu-
lar Filter-Bank Modulations" to be submitted.
International conferences
Accepted
1. B.Benammar, N.Thomas, C.Poulliat, ML.Boucheret, M.Dervin, "Asymptotic Analysis and Design of
Iterative Receivers for Non Linear ISI Channels" ISTC August 18-22, 2014, Bremen, Germany.
2. B.Benammar, N.Thomas, C.Poulliat, ML.Boucheret, M.Dervin, "On Linear Frequency Domain Turbo-
Equalization of Non Linear Volterra Channels" ISTC August 18-22, 2014, Bremen, Germany.
3. H.Abdulkader, B.Benammar, C.Poulliat, ML.Boucheret, N.Thomas, "Analysis and Design of Radial
Basis Function-Based Turbo Equalizers" ISTC August 18-22, 2014, Bremen, Germany.
4. H.Abdulkader, B.Benammar, C.Poulliat, ML.Boucheret, N.Thomas, "Neural Networks-Based Turbo
Equalization of a Satellite Communication Channel" SPAWC June 22-25, 2014, Toronto, Canada.
5. B.Benammar, N.Thomas, C.Poulliat, ML.Boucheret, M.Dervin, "On linear MMSE Based Turbo-equalization
of Nonlinear Satellite Channels" ICASSP May 26-31, 2013, Vancouver, Canada.
6. B.Benammar, N.Thomas, ML.Boucheret, C.Poulliat, M.Dervin, " Analytical expressions of Power Spec-
tral Density for General Spectrally Shaped SC-FDMA Systems" EUSIPCO Sep. 9-13, 2013, Marrakech,
Morocco.
vi
National conferences
1. B.Benammar, N.Thomas, C.Poulliat, ML.Boucheret, M.Dervin, "Turbo- Egalisation MMSE Lineaire De
Canaux Non Lineaires" GRETSI Sep. 3-6, 2013, Bretagne, France.
vii
viii
Abstract
Increasing both the data rate and power e�ciency of single carrier transmissions over broadcast satellite links
has become a challenging issue to comply with the urging demand of higher transmission rates. If emerging
transmission techniques encourage the use of high order modulations such as Amplitude and Phase Shift
Keying (APSK) and Quadrature Amplitude Modulation (QAM), some channel impairments arise due to on-
board satellite processing. Indeed, due to satellite transponder Power Ampli�ers (PA) as well as transmission
�lters, high order modulations incur non linear distortions due to their high envelope �uctuations which require
speci�c processing either at the transmitter or at the receiver.
In this thesis, we investigate on non linear interference mitigation at the receiver with a special focus on iterative
equalizers which dramatically enhance the performance at the cost of additional complexity. Based on the time
domain model of the non linear interference induced by the PA, optimal and sub-optimal receiving algorithms
are proposed and their performance compared. Low complexity implementations are also investigated for the
sake of a better complexity-performance trade-o�. Then, a non linear frequency domain model is derived and
the corresponding frequency equalizers are investigated.
In the second part, we analyse and design an iterative receiver for the non linear Inter Symbol Interference
(ISI) channel. The objective is to optimize an outer Low Density Parity Check (LDPC) code distribution
polynomials so as to best �t the inner equalizer Extrinsic information. The optimized receiver is shown to
achieve better performance compared to a code only optimized for linear ISI channel.
Finally, we investigate on a speci�c class of single carrier transmissions relying on Single Carrier Orthogonal
Frequency Division Multiplexing (SCO-FDM) for satellite downlink. The advantage of such waveforms lies
in their practical receiver implementation in the frequency domain. General analytical formulas of the power
spectral density and signal to noise and interference ratio are derived and used to predict the bit error rate for
frequency selective multiplexers.
ix
x
Abreviations
AM-AM Amplitude to Amplitude
AM-PM Amplitude to Phase
BCH Bose, Ray-Chaudhuri et Hocquenghem
BEC Binary Erasure Channel
BICM Bit Interleaved Coded Modulation
BP Belief Propagation
BPSK Binary Phase Shift Keying
CA Complex Adds
CC Convolutional Codes
CCDF Cumulative Complementary Density Function
CM Complex Multiplies
CN Check Node
DFT Discrete Fourier Transform
DVB-S Digital Video Broadcasting Satellite
ENGINES Enabling Next GeneratIon NEtworks for broadcast Services
ETSI European Telecommunications Standards Institute
EW-SC-FDM Extended Weighted Singe-Carrier Frequency Division Multiplexing
EXIT EXtrinsic Information Transfer
FET Field E�ect Transistor
xi
FIR Finite Impulse Response
FSS Fixed Services Satellite
GF Galois Field
GFDM Generalised Frequency Division Multiplexing
GM Gaussian Mixture
IBO Input Back-O�
IMUX Input MUltipleXer
LDPC Low Density Parity Check
MAP Maximum A Posteriori
MLSE Maximum Likelihood Sequence Equalizer
MMSE Minimum Mean Square Error
MSE Mean Square Error
MSS Mobile Services Satellite
OFDM Orthogonal Frequency Division Multiplexing.
OFDMA Orthogonal Frequency Division Multiple Access.
OMUX Output MUltipleXer
OBO Output Back-O�
PAPR Peak to Average Power Ratio
QAM Quadrature and Amplitude modulations
QPSK Quadrature Phase Shift Keying
RF Radio Frequency
RS Reed Solomon
SISO Soft Input Soft Output
SP Sum Product (SP)
SSPA Solid State Power Ampli�er
TT & C Telemetric Tracking and Command
TWTA Travelling Wave Tube Ampli�er
UE User Equipment
VN Variable Nodexii
Contents
Remerciements iii
Résumé v
Abstract ix
Abreviations xi
Introduction (French) 1
1 Digital communications over satellite channels 9
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2 Introduction (french) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3 Satellite communication system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4 Broadcasting Satellites standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.1 DVB-S standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.2 DVB-S2 standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4.3 DVB-S2X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.5 Transponder modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.1 TWT and SSP Ampli�ers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.2 Input and output multiplexers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.5.3 Saturation levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.6 Impact of system parameters on the non linear channel . . . . . . . . . . . . . . . . . . . . . . . 22
1.6.1 Impact of IBO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.6.2 Impact of the root raised cosine roll-o� . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
xiii
1.6.3 Impact of the signal bandwidth in the presence of IMUX and OMUX . . . . . . . . . . 24
1.7 Non linear satellite channel models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.7.1 Linear model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.7.2 Volterra model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.7.3 Volterra coe�cients design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.7.4 Volterra decomposition for test channels . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.8 Frequency domain Volterra model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.8.1 Multi-dimensional Fourier Transforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
1.8.2 Frequency domain Volterra model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
1.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.10 Conclusion (french) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2 Mitigation of non linear satellite channels interference 41
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.2 Introduction (French) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.3 Optimal time domain equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.3.1 Trellis based structure of the non linear channel . . . . . . . . . . . . . . . . . . . . . . . 43
2.3.2 Symbol based detection: MAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.3.3 Sequence based detection: MLSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.4 Linear time domain equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.5 Non linear sub-optimal equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.5.1 Non linear adaptive Volterra equalization . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.5.2 Decision Feedback Equalization: DFE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.6 Frequency domain equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.6.1 Linear MMSE -FD equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.6.2 Hybrid time and frequency domain DFE . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.7 Equalization schemes comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.7.1 Complexity comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.7.2 Performance comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.9 Conclusion (french) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
xiv
3 Iterative equalization and decoding 69
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.2 Introduction (French) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.3 Turbo equalization principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.4 Optimal SISO MAP equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.5 Linear MMSE turbo-equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.5.1 Linear MMSE time varying solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.5.2 No-Apriori (NA) MMSE approximation . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.5.3 Averaged Low Complexity (ALC) MMSE approximation . . . . . . . . . . . . . . . . . . 82
3.5.4 Frequency domain turbo linear MMSE equalizer . . . . . . . . . . . . . . . . . . . . . . 82
3.6 SISO MAP decoding over a trellis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.7 SISO LDPC decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.7.1 Useful notations and de�nitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.7.2 Belief Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.8 Comparison of iterative equalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.8.1 Complexity comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.8.2 Performance comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.9 Receiver asymptotic analysis and design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.9.1 Mutual information computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
3.10 Asymptotic code design using EXIT charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
3.10.1 Iterative receiver scheduling and interleaver assumptions . . . . . . . . . . . . . . . . . . 101
3.10.2 Code optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
3.10.3 Optimization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
3.11 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
3.12 Conclusions (French) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
4 SC-OFDM in satellite communications 109
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.2 Introduction (French) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.3 SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
4.3.1 Frequency based SC-OFDM scheme description . . . . . . . . . . . . . . . . . . . . . . . 113
4.3.2 Extended Weighted SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
xv
4.4 From frequency to time domain representation . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
4.4.1 Multi-rate FFT/IFFT noble identities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
4.4.2 Transmitter (Tx) equivalent model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.4.3 Receiver (Rx) modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4.4.4 Global system time domain equivalent model . . . . . . . . . . . . . . . . . . . . . . . . 119
4.4.5 EW-SC-OFDM as a circular convolution . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.4.6 Special cases of the general scheme: SC-OFDM and EW-SC-OFDM . . . . . . . . . . . 122
4.5 PSD analysis of SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.5.1 PSD with rectangular shaping : SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . 124
4.5.2 PSD with root raised cosine EW-SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.6 Linear equalization and SINR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.6.1 The useful term power Pu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4.6.2 The interfering term power σ2i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4.6.3 The noise power σ2w̃ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.6.4 SINR function of SNR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4.6.5 Linear equalizers: MMSE and ZF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4.7 Applications to the SINR of SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.7.1 SINR of SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.7.2 SINR of EW-SC-OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
4.9 Conclusion (French) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
5 Conclusions and future work 135
5.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
5.2 Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.2.1 Estimation canal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.2.2 Synchronisation horloge et porteuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.2.3 Bourrage de zéros ou bien cyclique pré�xe ? . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.2.4 Comparaison avec d'autres techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.2.5 Égalisation au sens large . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
5.2.6 Generalised Frequency division multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . 139
5.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
xvi
5.4 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
5.4.1 Channel estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
5.4.2 Frequency and clock synchronisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
5.4.3 Zero padding or cyclic pre�xing? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
5.4.4 Comparison with alternative techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
5.4.5 Widely linear equalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
5.4.6 Generalised Frequency division multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . 143
Appendices 147
A Analytical expressions of the power spectral density of SC-OFDM 147
B Equivalent noise variance 151
C On How to estimate the ellipse parameters of a non-circular noise 153
C.0.7 Ellipse characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
C.0.8 Application to a correlated noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
xvii
xviii
List of Figures
1.1 DVB-S functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2 DVB-S2 functional block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.3 Scatter plot of the DVB-S2 modulation γ = 2.85 and γ1 = 2.84 and γ2 = 5.27 . . . . . . . . . . 14
1.4 Structure of a Travelling Wave Tube Ampli�er . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.5 AM-AM characteristic using Saleh's model with parameters αa = 1.9638 and βa = 0.9945 . . . 18
1.6 AM-PM characteristic using Saleh's model with parameters αφ = 2.5293 and βφ = 2.8168 . . . 19
1.7 Gain for IMUX and OMUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.8 Group delay for IMUX and OMUX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.9 Satellite channel modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.10 Constellation for 16APSK with roll-o� α = 0.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.11 PDF of real and imaginary parts of one outer ring centroid at IBO = 0dB . . . . . . . . . . . . 24
1.12 PDF of real and imaginary part of one outer ring centroid at IBO = 9dB . . . . . . . . . . . . 25
1.13 Power spectral density of the ampli�ed signal for di�erent IBO values . . . . . . . . . . . . . . 26
1.14 ISI variance function of the root raised cosine roll-o� α . . . . . . . . . . . . . . . . . . . . . . . 27
1.15 Constellation warping for 16APSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1.16 Polynomial decomposition for AM-AM Saleh's function . . . . . . . . . . . . . . . . . . . . . . 32
1.17 Polynomial decomposition for AM-PM Saleh's function . . . . . . . . . . . . . . . . . . . . . . 33
1.18 Scatterplots of 16APSK with roll-o� α = 0.2 at IBO = 3dB . . . . . . . . . . . . . . . . . . . . 34
1.19 System model description in the frequency domain . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.1 Trellis representation of the non linear channel . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.2 DFE with linear feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.3 DFE with non linear feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.4 Hybrid Time and frequency time domain equalizer . . . . . . . . . . . . . . . . . . . . . . . . . 61
xix
2.5 Mean Square Error for the MMSE time domain equalizer function of the feed-forward �lter
lengths N1 and N2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.6 Number of complex MMSE operations for a block of estimated symbols L = 512 . . . . . . . . 66
2.7 Bit Error Rate performance of the equalizers over the channel test 2 . . . . . . . . . . . . . . . 67
3.1 Structure of a turbo equalizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.2 Iterative Volterra receiver for the non linear channel . . . . . . . . . . . . . . . . . . . . . . . . 73
3.3 Linear MMSE time domain solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.4 Estimation error PDF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.5 Common sub-matrix in the MMSE solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.6 SIC MMSE turbo FDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.7 Tanner graph representation of the LDPC code matrix H where (N = 8, dv = 2, dc = 4) . . . . 88
3.8 Belief propagation for a degree i VN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.9 Belief propagation for a degree j CN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
3.10 Complexity comparison for iterative receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.11 Performance comparison of the non linear channel iterative receivers . . . . . . . . . . . . . . . 93
3.12 Gaussian mixture LLRs for 16APSK rate 3/4 at Eb/N0 = 20dB . . . . . . . . . . . . . . . . . . 97
3.13 EXIT charts for the AWGN 16APSK BICM soft demapper . . . . . . . . . . . . . . . . . . . . 98
3.14 Mutual Information for the 16APSK-BICM soft demapper using di�erent approximations . . . 100
3.15 The function Ψ(σ) and its inverse Ψ−1(Ie) for 16-APSK BICM . . . . . . . . . . . . . . . . . . 101
3.16 Mutual Information for the 16APSK-BICM MAP and MMSE equalizers for test channel 2 . . . 102
3.17 Global scheme of a satellite communication channel. GM stands for quantities with a Gaussian
Mixture approximation, G for Gaussian approximation . . . . . . . . . . . . . . . . . . . . . . . 102
3.18 Partial and ensemble interleaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
3.19 Achievable designed rates compared with the MAP optimal equalizer and the 16-APSK ISI-free
rates for a maximum dv = 10 over the test channel 2 . . . . . . . . . . . . . . . . . . . . . . . . 105
3.20 Achievable designed rates compared with the NA-MMSE equalizer and the 16-APSK ISI-free
rates for a maximum dv = 10 over the test channel 2 . . . . . . . . . . . . . . . . . . . . . . . . 105
3.21 Bit error rate for the iterative receivers and the optimized LDPC code . . . . . . . . . . . . . . 106
4.1 IMUX/OMUX responses for di�erent symbol rates . . . . . . . . . . . . . . . . . . . . . . . . . 112
4.2 SC-FDMA and SC-OFDM frequency based representation . . . . . . . . . . . . . . . . . . . . . 113
4.3 EW-SC-OFDM transmission scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
4.4 Exteding from a length M to U ≤ 2M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
xx
4.5 CCDF of INP for SC-OFDM, EW-SC-OFDM (roll-o�s 0.05 and 0.25) and OFDM usingN = 512
and M = 432 with an oversampling factor 4 for 16APSK . . . . . . . . . . . . . . . . . . . . . . 116
4.6 Up-sampling identity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.7 Down-sampling identity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4.8 An example of stacking with L = 8, N = 4, and LN = 2 . . . . . . . . . . . . . . . . . . . . . . 117
4.9 Localised mapping modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.10 Transmitter equivalent model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.11 Localised demapping and equalization equivalent model . . . . . . . . . . . . . . . . . . . . . . 119
4.12 Receiver equivalent model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4.13 SC-OFDM equivalent frequency domain system model . . . . . . . . . . . . . . . . . . . . . . . 120
4.14 SC-OFDM equivalent time domain system model . . . . . . . . . . . . . . . . . . . . . . . . . . 120
4.15 Receiver structure of SC-OFDM using spectral shaping of length U ≥M . . . . . . . . . . . . . 1214.16 Spectral shaping �lter with root raised cosine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
4.17 Transmitter model of SC-OFDM with pulse shaping . . . . . . . . . . . . . . . . . . . . . . . . 123
4.18 PSD EW-SC-OFDM with M = 426, N = 512, and α = 0 . . . . . . . . . . . . . . . . . . . . . 124
4.19 PSD EW-SC-OFDM with M = 426, N = 512, and α = 0.25 . . . . . . . . . . . . . . . . . . . . 125
4.20 SC-OFDM simpli�ed system model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.21 Equivalent noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.22 MMSE and ZF SINR for EW-SC-OFDM N = 512, M = 426, and α = 0.05 . . . . . . . . . . . 132
4.23 MMSE and ZF BER for EW-SC-OFDM N = 512, M = 426, and α = 0.05 . . . . . . . . . . . . 133
5.1 EW-SC-OFDM with roll-o� α = 0.05, N = 512 and M = 426 . . . . . . . . . . . . . . . . . . . 138
5.2 Time domain GFDM system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
C.1 Approximations to the .99th quantile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
C.2 Approximations to the .90th quantile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
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xxii
List of Tables
1.1 DVB-S2 modulation schemes parameters for QPSK, 8PSK, 16APSK and 32ASPK . . . . . . . 15
1.2 Optimum constellation radius ratio for AWGN channel with 16APSK . . . . . . . . . . . . . . 15
1.3 Optimum constellation radius ratio for AWGN channel with 32APSK . . . . . . . . . . . . . . 16
1.4 Comparative characteristics for TWTA and SSPA . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.5 ISI variance for di�erent signal bandwidths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.6 Table of MSE for di�erent polynomial order decompositions . . . . . . . . . . . . . . . . . . . . 32
1.7 Test channels characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.8 Volterra kernels for test channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.1 Comparison of linear and non linear Volterra channel equalizers . . . . . . . . . . . . . . . . . . 64
3.1 Approximation parameters for the J and J−1 function . . . . . . . . . . . . . . . . . . . . . . . 95
3.2 Gaussian Mixture parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.1 Values for the over-all channel number of symbol spaced taps . . . . . . . . . . . . . . . . . . . 112
4.2 Simulation parameters for SC-OFDM and EW-SC-OFDM . . . . . . . . . . . . . . . . . . . . . 131
xxiii
xxiv
Introduction (French)
Pendant plus d'un demi siècle, les systèmes satellites ont acheminé et transporté des données vers des con-
trées lointaines et sur des zones étendues. Que ce soit pour les télécommunications, le positionnement ou
l'observation de la terre, l'augmentation des débits des communications par satellite revêt une importance
majeure dans les évolutions futures de ces technologies.
Lorsqu'il s'agit de développer un système de communication, plusieurs paramètres entrent en jeu a�n de di-
mensionner les capacités des liens. Plus précisément, en fonction de la nature du service rendu par le satellite
(�xe, mobile, di�usion), du sens de la communication (liaison montante ou descendante), de la bande passante
disponible ainsi que de la complexité permise, les solutions permettant d'augmenter le débit et l'e�cacité en
puissance peuvent di�érer.
L'e�cacité en puissance mesure la robustesse face aux perturbations du bruit et est souvent liée à la distance
minimale du code et de la modulation utilisés. L'e�cacité spectrale quant à elle, caractérise le débit de la
communication pour une bande donnée et est reliée à la cardinalité de la modulation ainsi qu'au rendement de
codage. Il existe en général un compromis entre e�cacité en puissance et e�cacité spectrale. Cependant, de
nouvelles avancées dans le domaine des traitements itératifs ont permis de réduire ce compromis en exploitant
un degré de liberté supplémentaire qui est celui de la complexité.
Dans cette thèse, nous nous positionnons au niveau de la voie descendante d'un système de di�usion par satel-
lite. Pour une telle application, l'élément dimensionnant est le transpondeur à bord du satellite qui comprend
les �ltres multiplexeurs ainsi que l'ampli�cateur de puissance. En e�et, puisque le satellite est contraint en
termes de consommation de puissance et d'interférence sur les canaux adjacents, le transpondeur est ainsi "le
goulot" de l'optimisation du système. Nous étudions donc deux techniques permettant d'augmenter les débits
du système et évaluons leur impact sur les éléments du transpondeur.
D'une part, l'utilisation de modulations d'ordre élevé permet d'augmenter le nombre de bits transmis par utili-
sation du canal, mais entraine pour les modulations d'amplitude et de phase une augmentation de la �uctuation
1
2 Introduction
de l'enveloppe du signal. Ceci donne lieu à de l'interférence non linéaire quand ces signaux sont traités par un
ampli�cateur de puissance opérant à saturation (ou proche de la saturation). Ce type d'interférence est aussi
rencontré dans d'autres applications telles que les canaux à enregistrement magnétique ou les communications
par �bre optique. D'autre part, augmenter les débits utiles peut aussi être réalisé, en augmentant le débit du
signal. Cependant, si la bande du signal dépasse celle des �ltres multiplexeurs, la sélectivité en fréquence du
canal satellite est augmentée, générant une interférence additionnelle à la réception.
Pour les deux techniques d'augmentation de l'e�cacité spectrale, une analyse de la nature et de la quantité
d'interférence est nécessaire a�n d'adopter les méthodes de réduction d'interférences adéquates. Les traite-
ments peuvent ainsi être envisagés au niveau de l'émetteur au travers de techniques dites de pré-compensation
ou de pré-distorsion, ou au niveau du récepteur par des techniques dites d'égalisation. Dans cette thèse nous
nous intéressons plus particulièrement à l'analyse et l'optimisation des récepteurs itératifs pour le canal non
linéaire, ainsi qu'aux formes d'ondes nouvelles permettant des algorithmes de réception plus e�caces.
Structure du manuscrit
Cette thèse s'articule en quatre chapitres principaux dont voici les descriptifs:
• Chapitre 1: Ce chapitre présente une description du système satellite surle quel notre étude portera.Il s'agit d'un système de di�usion par satellite et plus spéci�quement du standard de di�usion vidéo
numérique (DVB). Nous présentons les nouvelles modulations proposées dans le standard DVB-S2 qui
permettent d'atteindre un compromis intéressant entre e�cacité en puissance et e�cacité spectrale. Nous
étudions ensuite les éléments constituants du transpondeur à bord du satellite, en évaluant l'impact de
paramètres tels que le roll-o� des �ltres, la bande du signal, les reculs de l'ampli�cateur sur la quantité
et la forme de l'interférence reçue. Ensuite, nous présentons un modèle de l'interférence non linéaire
au rythme symbole en nous basant sur une décomposition en somme in�nie dite de Volterra. Pour des
raisons de complexité, ce modèle est tronqué aux raisonnables troisième et cinquième ordres, et l'impact
de cette troncature sur la précision du modèle est évalué. En�n, le modèle fréquentiel équivalent de la dé-
composition en séries de Volterra est décrit et sera utilisé ultérieurement pour les traitements fréquentiels.
• Chapitre 2: Ce chapitre traite des égaliseurs non itératifs pour le modèle non linéaire du canalsatellite. Dans un premier temps, nous présentons une description sous forme de chaîne de Markov des
non linéarités qui permet de dériver des égaliseurs optimaux au sens symbole et séquence. En raison
3
de la complexité exponentielle de ces égaliseurs, nous étudions des égaliseurs sous optimaux linéaires et
non linéaires. Plus précisément, nous développons les expressions d'égaliseurs linéaires qui minimisent
l'erreur quadratique moyenne ainsi que deux égaliseurs non linéaires à retours de décision. Ensuite,
d'une manière similaire au domaine temporel, nous présentons des expressions d'égaliseurs linéaires et
non linéaires fréquentiels. Nous dérivons ainsi de nouveaux résultats concernant l'égalisation hybride
temps-fréquence pour le canal de Volterra. En�n, ces di�érentes implémentations sont comparées en
termes de taux d'erreurs binaires et de complexité.
• Chapitre 3: Ce chapitre présente des résultats sur la turbo égalisation du canal non linéaire satellite.Premièrement, nous rappelons des résultats sur l'égalisation itérative optimale pour des canaux décrits
par un treillis, ce qui est le cas du canal nonlinéaire modélisé par une série de Volterra. Ensuite, nous
dérivons des expressions pour les égaliseurs linéaires basés sur le modèle de Volterra, et étudions les
approximations à faible complexité de ces égaliseurs. Par ailleurs, nous analysons l'égalisation itérative
fréquentielle du canal de Volterra. Dans un second temps, nous concevons et optimisons le code canal qui
permet de s'adapter au mieux aux messages issus de l'égaliseur en utilisant la méthode d'ajustement de
la courbe (curve �tting) en utilisant l'outil EXIT. Pour ce faire, nous modélisons la sortie de l'égaliseur
par un mélange de Gaussiennes qui est plus adéquat que l'approximation Gaussienne pour des modula-
tions non binaires. En�n, nous illustrons les gains en termes de taux d'erreurs binaires des codes ainsi
optimisés en comparaison avec des codes non optimisés.
• Chapitre 4: Dans le chapitre 4, nous étudions la seconde méthode permettant d'améliorer les débits,et ce en élargissant la bande du signal aux dépens d'une augmentation de la sélectivité en fréquence des
�ltres à bord du satellite. A�n de réduire les interférences issus de cette augmentation de bande, nous
présentons une forme d'onde permettant des traitements fréquentiels simpli�és. Cette forme d'onde a
les avantages d'une modulation mono-porteuse en termes de �uctuations d'enveloppe, et les avantages
d'une modulation multi-porteuses en termes d'égalisation fréquentielle simpli�ée. Dans le cadre de notre
étude, nous présentons un modèle fréquentiel et son équivalent en temporel pour cette forme d'onde, ce
qui permet de dériver des formules analytiques de densité spectrale de puissance. De plus, nous étudions
les interférences résiduelles après égalisation linéaire et dérivons des formules analytiques de rapport
signal à bruit plus interférences qui nous permettent de prédire les performances du système.
4 Introduction
Contributions principales
Les contributions principales de cette thèse sont résumées comme suit:
• Chapitre 1: Nous étudions l'impact des paramètres du système sur la représentation en série de Volterrade l'interférence non linéaire du canal satellite. Nous dérivons aussi un modèle, en nous basant sur des
paramètres souhaités du système, qui constituera notre canal de test plus tard dans le manuscrit.
• Chapitre 2: Nous dérivons des égaliseurs temporels et fréquentiels linéaires et non linéaires du canal deVolterra et comparons les complexités. Nous présentons de nouveaux résultats sur l'égalisation hybride
temps-fréquence appliquée au modèle de Volterra.
• Chapitre 3: Nous présentons l'égalisation itérative linéaire dans le domaine temporel [Benammar et al., 2013b]ainsi que dans le domaine fréquentiel [Benammar et al., 2014a]. Nous modélisons les sorties de l'égaliseur
par un mélange de Gaussiennes dont nous dérivons les paramètres pour de la détection sur un canal
Gaussien. Cette approximation est utilisée pour l'optimisation du code canal que nous appliquons à
di�érentes classes d'égaliseurs optimaux [Benammar et al., 2014b] et sous-optimaux.
• Chapitre 4: Nous dérivons un modèle temporel généralisé de la forme d'onde mono porteuses parmultiplexage à division orthogonale en fréquence (SC-OFDM). Nous proposons en outre des formules
analytiques de la densité spectrale de puissance [Benammar et al., 2013a] et du rapport signal à bruit
plus interférences pour ce type de forme d'ondes.
5
Introduction
For more than half a century, satellite systems have been conveying data over large and remote areas. Providing
high throughput satellite communications is a challenging aspect in the evolutions of next generation satellite
technologies be it for telecommunications, positioning or earth observation, .
When designing communication systems, many features interplay in dimensioning the link capacities. More
speci�cally, depending on the nature of the satellite service (�xed, mobile, broadcast), the transmission link
(up or down-link), the available bandwidth, and the acceptable complexity, solutions providing high spectral
and power e�cient satellite communications may di�er.
The power e�ciency measures the robustness to noise impairments and is usually related to the minimum
distance of the code and modulation. The spectral e�ciency characterises the communication throughput
per occupied bandwidth and thus is related to the cardinality of the modulation and the rate of channel
coding. There usually exists a trade-o� between achieving a good power and spectral e�ciency simultaneously.
However, emerging advances in iterative processing have allowed reducing this trade-o� by exploiting an
additional degree of freedom which is the system complexity. In this thesis, we position ourselves in the forward
link of a broadcast satellite system. For such a system, the key component is the satellite transponder which
comprises multiplexing �lters and the satellite ampli�er. Indeed, since there are constraints on the available
power and the maximum adjacent channel interference allowed, the transponder is usually the bottleneck in the
design of broadcasting satellite systems. We thus investigate the impact of using two methods for increasing
the throughput on the satellite transponder and thus on the overall system performance.
On the one hand, increasing the throughput by using high order modulations yields to higher signal �uctuations
which give rise to non linear interference when the signals are ampli�ed by a nearly saturated satellite ampli�er.
This kind of interference is also encountered in magnetic recording channels and �ber optical communications.
On the other hand, increasing the throughput can also be carried out by increasing the symbol rate. Thus,
the signal bandwidth may exceed the satellite multiplexing �lters bandwidths leading to increased frequency
selectivity in the satellite channel.
For both scenarios, an analysis of the nature and amount of interference is necessary in order to adopt adequate
processing. Mitigation of the satellite channel impairments can be carried out either at the transmitter through
pre-compensation and/or pre-distortion, or at the receiver by means of equalization. In this thesis, we are
interested in receiver design for non linear satellite channels and the advanced waveforms allowing for a more
e�cient equalization at the receiver.
6 Introduction
Structure of the manuscript
• Chapter 1: This chapter presents a description of the satellite systems under study. We are interestedin broadband satellite services and more speci�cally in the Digital Video and Broadcasting standards.
We present the DVB-S2 Amplitude and Phase Shift Keying schemes as well as related channel coding.
We then present the satellite transponder constituting components, and show the impact of some system
parameters such as the �lters roll-o�s, the signal bandwidth and the input back-o� on the behaviour of
the transponder. Moreover, we derive analytical symbol based description of the non linear interference
by means of in�nite Volterra series. For complexity considerations, this decomposition is truncated to
reasonable third and �ve orders and the impact of this truncation on the model accuracy is analysed.
Last but not least, we present the frequency domain equivalent Volterra series decomposition which is
used later in the manuscript for frequency domain based processing.
• Chapter 2: This chapter deals with non iterative equalization for the non linear Volterra satellite chan-nel. In the �rst part, we present a Markov chain description of the Volterra channel which then allows for
the derivation of optimal symbol and sequence equalization. Due to the exponential complexity of the
optimal equalizers, we investigate on sub-optimal linear and non linear equalization schemes in the time
domain. More speci�cally, we derive expressions for the linear Minimum Mean Square Error estimator
and two non linear Volterra decision feedback equalizers for the non linear channel. Then, similarly to
the time domain, we present frequency domain linear and non linear equalization schemes. We speci�-
cally derive novel results on the hybrid time and frequency domain equalizer. Then, we compare these
implementations in terms of bit error rates and complexity.
• Chapter 3: This chapter addresses iterative equalization and decoding for the non linear satellitechannel. In the �rst part, we remind results on optimal iterative equalization for channels described
by a trellis which we have shown to be the case of the Volterra non linear channel. Then, we derive
novel results on time domain linear iterative equalizers based on the Volterra channel, and investigate
on lower complexity approximations for the linear equalizer. We also analyse the frequency domain low
complexity iterative equalizers. In a second part, we design and optimize the channel code so as to �t
the equalizers output by the EXIT-chart curve �tting technique. To do so, we model the output of the
equalizer as a mixture of Gaussians which we show is more accurate than the Gaussian approximation.
Finally we illustrate the improvement in error rates for these approximations in comparison with non
7
optimized receivers.
• Chapter 4: In the chapter 4, we address the second throughput increasing technique relying on en-larging the signal bandwidth at the expense of increased frequency selectivity. Thus, to e�ciently cope
with the generated interference, we present a suitable single carrier transmission scheme which allows for
simple frequency domain equalization at the receiver. We present both a frequency domain and a novel
time domain model for this single carrier modulation which allows us to investigate on the spectrum
characteristics and derive analytical expressions for its spectral density. Moreover, we investigate on the
residual interference when linear equalizers are used and derive analytical expressions for the signal to
interference and noise ratio, which allows for a good prediction of the system performance.
Main contributions
The main contributions of this thesis can be summarised as follows:
• Chapter 1: We study of the impact of the system parameters on the representation of the non linearsatellite channel by Volterra series, and derive a test channel model given some system parameters which
will be used later in simulations.
• Chapter 2: We derive a novel hybrid time and frequency domain equalizer for the Volterra descriptionof the non linear interference and a detailed complexity analysis for di�erent classes of equalizers.
• Chapter 3: We investigate on iterative linear time domain MMSE equalization [Benammar et al., 2013b]and frequency domain equalizers for the non linear satellite channel [Benammar et al., 2014a].
We also model the output of the equalizer as a Gaussian Mixture instead. This approximation is used
in the code design and optimization for a class of optimal and sub-optimal iterative receivers for the non
linear channel [Benammar et al., 2014b].
• Chapter 4: We derive a time general representation of the Single Carrier -Orthogonal Frequency DivisionMultiplexing (SC-OFDM) modulation. We also derive analytical expressions for the spectral density
[Benammar et al., 2013a] and signal to interference noise ratio for SC-OFDM.
8 Introduction
Chapter 1
Digital communications over satellite
channels
Contents1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2 Introduction (french) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3 Satellite communication system . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4 Broadcasting Satellites standards . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.1 DVB-S standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121.4.2 DVB-S2 standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.4.3 DVB-S2X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.5 Transponder modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.1 TWT and SSP Ampli�ers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161.5.2 Input and output multiplexers . . . . . . . . . . . . . . . . . . . . . . . . . . 201.5.3 Saturation levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.6 Impact of system parameters on the non linear channel . . . . . . . . . . 22
1.6.1 Impact of IBO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221.6.2 Impact of the root raised cosine roll-o� . . . . . . . . . . . . . . . . . . . . . 231.6.3 Impact of the signal bandwidth in the presence of IMUX and OMUX . . . . 24
1.7 Non linear satellite channel models . . . . . . . . . . . . . . . . . . . . . . . 25
1.7.1 Linear model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261.7.2 Volterra model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281.7.3 Volterra coe�cients design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301.7.4 Volterra decomposition for test channels . . . . . . . . . . . . . . . . . . . . . 33
1.8 Frequency domain Volterra model . . . . . . . . . . . . . . . . . . . . . . . 34
1.8.1 Multi-dimensional Fourier Transforms . . . . . . . . . . . . . . . . . . . . . . 351.8.2 Frequency domain Volterra model . . . . . . . . . . . . . . . . . . . . . . . . 36
1.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.10 Conclusion (french) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
9
10 Chapter 1 - Digital communications over satellite channels
1.1 Introduction
New generation satellite broadcasting trends recommend using high order modulations to increase the spectral
e�ciency of the satellite link. Such high order modulations can be designed to allow a better resistance to
noise (compared to amplitude shift keying), such as the new modulations suggested in the second generation
broadcasting system. However, increasing the power e�ciency does not come at no cost, since the resulting new
waveforms have higher signal dynamics. This increased �uctuation has a direct impact on the operating region
of non linear ampli�ers on board satellites. Indeed, if the signal has large �uctuations, a non negligible back-o�
is required to the saturation power of the ampli�er. The introduced back-o�s decrease the energy e�ciency
of the power ampli�er and thus impacts the overall link budget. If instead small back-o�s are considered
despite the large signal dynamics, the ampli�ed signal is distorted and unless suitable mitigation techniques
are used, the link budget is again impacted. It is thus important to understand the di�erent technical issues
involving the use of high order modulations and the corresponding RF design challenges. To do so, we start
by introducing the context of satellite broadcasting systems. We then study the impact of di�erent system
con�gurations on the distortions induced by the non linear power ampli�er. Then, we develop an analytical
symbol based model for these distortions. Finally we investigate on equivalent representations of the non linear
channel in the frequency domain, which will help us later develop frequency domain mitigation techniques.
1.2 Introduction (french)
Les nouvelles tendances concernant la di�usion par satellites, suggèrent l'utilisation de schémas de modulations
d'ordre élevé a�n d'améliorer l'e�cacité spectrale des communications par satellites. Ces modulations d'ordre
élevé peuvent être conçues a�n de permettre une meilleure résistance au bruit (comparées aux modulations
d'amplitude) à l'instar des modulations proposées dans la seconde génération des systèmes de di�usion. Cepen-
dant, l'amélioration de l'e�cacité en puissance n'est pas gratuite, puisque les nouvelles formes d'ondes ainsi
générées ont une plus forte dynamique du signal. Cette �uctuation additionnelle a un impact direct sur la zone
de fonctionnement des ampli�cateurs non linéaires présents à bord des satellites. En e�et, si le signal a une
forte �uctuation, un recul non négligeable vis à vis de la puissance de saturation est nécessaire. Ceci représente
un inconvénient majeur, puisque ces reculs diminuent l'e�cacité énergétique des ampli�cateurs, et in�uent sur
le bilan de liaison global. Si par contre, de faibles reculs par rapport à la puissance de saturation sont utilisés,
le signal ampli�é est distordu et à défaut de techniques adéquates d'élimination de ces distorsions, le bilan de
liaison est impacté. A�n d'illustrer les enjeux liés à ces nouvelles modulations, nous commencerons par une
1.3 - Satellite communication system 11
introduction des systèmes de di�usion par satellite. Nous étudierons ensuite l'e�et de certains paramètres sur
les distorsions générées par le canal nonlinéaire. Nous présenterons ensuite un modèle analytique au rythme
symbole pour ces distorsions. Finalement, nous éudierons une représentation équivalente de ce modèle dans le
domaine fréquentiel, ce qui nous permettra plus tard de développer des méthodes de traitement des distorsions
dans le domaine fréquentiel.
1.3 Satellite communication system
A classical transparent satellite communication system consists of three distinct blocks:
• The ground station which is usually referred to as the hub.It consists for uplink communications of a transmitting dish or antenna fed by signals aggregated from
di�erent baseband signals. A power ampli�er is used to cope with the sharp attenuation incurred by
the transmitted signal when propagating through long distances to the satellite.
• The satellite or the space segment.It consists of three di�erent components namely, the fuel component responsible for the propulsion, the
Telemetric Tracking and Command (TT & C) system and the communication payload which usually
contains several transponders. The TT & C system is used for all operations and commands concerning
the deployment and the maintenance of the satellite in orbit. The transponder generally designated by
the payload is responsible for all communications with the outside environment and thus for the Radio
Frequency (RF) communications.
Satellites can be classi�ed into Fixed Satellite Services (FSS), Mobile Satellite Services (MSS) and
Broadband Satellite Services (BSS). In this thesis, we focus on BSS systems with transparent satellites
which unlike regenerative satellites do not demodulate the baseband signal but only repeat the incoming
RF signal to the appropriate downlink channel with power ampli�cation.
• The receiving station which can be a ground station, individual antennas or terminals directly locatedat the customer. For television applications, the satellite broadcasts signals over a wide area which can
then be received by a large number of users with the use of small receiving antennas.
For satellite communications, the satellite transponder is generally the bottleneck of the system design, since
it has limited resources and thus any required base-band processing should be located either at the transmitter
station or at the receiving station.
12 Chapter 1 - Digital communications over satellite channels
Figure 1.1: DVB-S functional block diagram
1.4 Broadcasting Satellites standards
Broadcasting satellites are usually located in the geostationary orbit at about 37.000 km. The European
Telecommunications Standards Institute (ETSI) committee has issued many standards regulating satellite
broadcasting, depending on the type of the conveyed data.
Among the technologies of satellite broadcasting standards, we are interested in this thesis in Digital Video
Broadcasting (DVB) standards and more speci�cally in DVB-S its 2nd generation evolution DVB-S2.
1.4.1 DVB-S standard
The standardised DVB-S [EN, 1997] is illustrated in Figure 1.1. It o�ers a 36MHz communication channel
bandwidth and uses power e�cient modulations namely the Binary Phase Shift Keying (BPSK) and Quadra-
ture Phase Shift Keying (QPSK). Concatenated error correcting codes are used for channel coding. The
inner code is based on a set of punctured Convolutional Codes (CC) constructed from a 1/2-rate convolu-
tional code with constraint length equal to 7. The outer code is a shortened (N,K) Reed Solomon (RS) code
(N = 204,K = 188, T = 8) constructed on the Galois Field GF (28) from a RS code (N = 255,K = 239, T = 8)
where is the length of the codewords, and K is the length of the information symbols and T is the correction
capacity. It should be noted that the RS code shortening is realised by appending 51 null bytes to each block
of 188 bytes and discarded at the end of the coding/decoding process. Since the RS code is systematic, the null
bytes can be easily inserted and discarded at both ends of the coder and decoder. A convolutional interleaver
is inserted between the two channel codes to o�er a better correction capacity to the overall concatenated
channel code.
1.4.2 DVB-S2 standard
The DVB-S2 standard depicted in Figure 1.2 has been proposed as a spectrally and power e�cient transmission
technology through using Amplitude and Phase Shift Keying (APSK) modulations and a class of capacity
approaching block codes: Low Density Parity Check (LDPC) codes. The achieved system capacity gain over
1.4 - Broadcasting Satellites standards 13
Figure 1.2: DVB-S2 functional block diagram
the �rst generation DVB-S can reach 30%. Additionally, compared to the DVB-S standard, DVB-S2 o�ers
the possibility of adapting the modulation and coding formats to the link quality with the so-called Adaptive
Coding and Modulation (ACM) functionality.
DVB-S2 modulation schemes
The APSK modulation has been introduced in the DVB-S2 standard for its good trade-o� between spectral and
power e�ciency. Indeed, for an equivalent spectral e�ciency η, the APSK modulation has better robustness to
Gaussian noise compared to PSK modulation. This power e�ciency gain is achieved through dispatching the
symbols over multiple rings allowing a better separation distance between symbols and yet carrying equivalent
number of bits per modulated symbol. However, when compared to Quadrature an Amplitude modulations
(QAM) constellations, APSK is less noise resistant but o�ers lower signal �uctuations which is a valuable
feature especially for power ampli�ers. Since APSK modulation symbols are distributed over multiple rings,
it is convenient to de�ne the ratio γ which characterises the relation between modulations radii. As such, for
a 16APSK which consists of two concentric rings, the ratio γ writes as:
γ =R2R1
(1.1)
where R2 and R1 are the outer and inner rings radii respectively. For a 32APSK, the DVB-S2 standard de�nes
two ratios namely γ1 and γ2 describing the pairwise ratios and writing as follows:
γ1 =R2R1
and γ2 =R3R2
(1.2)
where R3, R2 and R1 are the outer, intermediate and inner rings radii respectively. An illustration of the
di�erent proposed modulation schemes can be found in Figure 1.3. The modulation symbols si for these
schemes can be written in a generic form as follows, :
si = Rn exp(j2πφk)fori = 1 : M (1.3)
where Rn is one of the radii of the modulation scheme and φk is one of the allowed modulation phases for the
ring radius Rn. Table 1.1 presents the di�erent radii and phases for DVB-S2 mapping sets. The mapping used
14 Chapter 1 - Digital communications over satellite channels
−1 0 1−1
−0.5
0
0.5
1Q
uadr
atur
e
QPSK
−0.5 0 0.5
−0.5
0
0.5
Qua
drat
ure
8PSK
−2 0 2
−2
−1
0
1
2
Qua
drat
ure
In−Phase
16 APSK
−5 0 5
−5
0
5
Qua
drat
ure
In−Phase
32 APSK
Figure 1.3: Scatter plot of the DVB-S2 modulation γ = 2.85 and γ1 = 2.84 and γ2 = 5.27
for PSK modulation is a Gray mapping whereas the mapping used for APSK modulations is a quasi-Gray
mapping. It is important to notice that the performance of the APSK modulation, depends on the ratios
γi, the number of constellation symbols on each ring, and the phase o�sets between symbols. The minimum
distance which measures the robustness to noise can be optimized to yield the targeted performance.
DVB-S2 coding schemes
The inner code of the DVB-S2 channel consists of a class of capacity approaching codes namely the LDPC
codes. The proposed code is systematic with KLDPC input bits and NLDPC coded bits. The standard
suggests two frame lengths consisting of short frames of length NLDPC = 16200 and long frames of length
NLDPC = 64800.
The outer code is a Bose, Ray-Chaudhuri et Hocquenghem (BCH) block code with parameters (NBCH ,KBCH , T )
where T is the correction capacity of the code. A block interleaver is used between the two channel codes to
cope with burst errors. This interleaver writes input stream in a matrix column-wise, and reads the elements
line-wise. The dimensions of the interleaver matrix are given in [EN, 2009] for normal and short frames.
1.4 - Broadcasting Satellites standards 15
Radii Phases Mapping in decimal
QPSK R = 1 k π2 +π4 [0, 2, 3, 1]
8PSK R = 1 k π4 +π4 [0, 4, 6, 2, 3, 7, 5, 1]
16APSK R1 = 1 kπ2 +
π4 [12, 14, 15, 13]
R2 = γ kπ6 +
π12 [4, 0, 8, 10, 2, 6, 7, 3, 11, 9, 1, 5]
32APSK R1 = 1 kπ2 +
π4 [17, 21, 23, 19]
R2 = γ1 kπ6 +
π12 [16, 0, 1, 5, 4, 20, 22, 6, 7, 3, 2, 18]
R3 = γ1γ2 kπ8 [24, 8, 25, 9, 13, 29, 12, 28, 30, 14, 31, 15, 11, 27, 10, 26]
Table 1.1: DVB-S2 modulation schemes parameters for QPSK, 8PSK, 16APSK and 32ASPK
Code rate Modulation coding/spectral e�ciency γ
2/3 2, 66 3, 15
3/4 2, 99 2, 85
4/5 3, 19 2, 75
5/6 3, 32 2, 70
8/9 3, 55 2, 60
9/10 3, 59 2, 57
Table 1.2: Optimum constellation radius ratio for AWGN channel with 16APSK
In [De Gaudenzi et al., 2006], the overall DVB-S2 system has been optimized to yield the best system ca-
pacity. To do so, the radii of APSK modulations was jointly optimized with the coding rate to yield the
best spectral e�ciency. Table 1.2 and Table 1.3 summarize the designed optimal ratios γ and (γ1, γ2) for the
couples (coding rate, spectral e�ciency).
1.4.3 DVB-S2X
DVB-S2X [DVB-S2X, 2014] is an evolution of the standard DVB-S2 which relies on the same physical layer
characteristics regarding the types of modulations and channel codes. However, there are some di�erences in
the system parameters which can be summarised as follows:
• Small roll-o�s (0.05 and 0.1) can be used leading to up to 15% gain in the system throughput.
• Finer modulations and coding rates
• The modulation ring ratios can be jointly chosen with coding rates for given ampli�er back-o�s.
16 Chapter 1 - Digital communications over satellite channels
Code rate Modulation coding/spectral e�ciency γ1 γ2
3/4 3, 74 2, 84 5, 27
4/5 3, 99 2, 72 4, 87
5/6 4, 15 2, 64 4, 64
8/9 4, 43 2, 54 4, 33
9/10 4, 49 2, 53 4, 30
Table 1.3: Optimum constellation radius ratio for AWGN channel with 32APSK
Using amplitude and phase shift keying modulations as originally proposed in the DVB-S2 standard has
given rise to some challenges related to power ampli�ers e�ciency. Power ampli�ers are located both at
the transmitter (ground station) and on-board satellites. Yet, since there are less restrictions on the power
supply of a hub or a gateway on a forward link, the limiting power ampli�er is the one located in the satellite
transponder. For a better understanding of the ampli�ers e�ects, we present in the next section the satellite
transponder constituent elements and how they impact the channel non linearity.
1.5 Transponder modelling
In this section we are interested in the elements constituting a transponder, and more speci�cally, the power
ampli�er and the input and output multiplexers. The considered ampli�er is a memory-less device with a
frequency independent ampli�cation model. The input and output multiplexers placed before and after the
power ampli�er are meant to reject undesired spectral components. In the following, we give more insights on
the classes of ampli�ers and the multiplexing �lter responses.
1.5.1 TWT and SSP Ampli�ers
TWTA
Travelling Wave Tube Ampli�er (TWTA) are wideband microwave ampli�ers capable of amplifying a wide
range of frequencies. Figure 1.4 depicts the structure of a TWT ampli�er.
A cathode heated at thousands of degrees generates an electron beam which is accelerated by the anode using
a high potential. These electrons propagate into a vacuum cavity containing a helix related to RF inputs and
outputs. The interaction between the RF signal and the electron beam leads to a deceleration of the electrons,
whose kinetic energy is transferred to the RF signal which is then ampli�ed. At the end of their race, electrons
1.5 - Transponder modelling 17
Figure 1.4: Structure of a Travelling Wave Tube Ampli�er
are captured by the collector which receives the remaining electrons energy. TWTA have interesting high gain
and low noise characteristics which makes them suitable for RF ampli�cation [Gilmour, 2011].
The ampli�cation process of a TWTA is usually described using two functions: Amplitude to Amplitude (AM-
AM) and Amplitude to Phase (AM-PM). Theses functions relate the input amplitude to the output amplitude
and phase rotation respectively. To describe a TWTA, Saleh in [Saleh, 1981] presented a frequency-independent
model to characterise the AM-AM and AM-PM functions of a TWTA. The derived frequency-independent
model of the ampli�er only depends on the instantaneous input amplitude r. The AM-AM and AM-PM
functions write as follows [Saleh, 1981]:
AM −AM(r) = αar1 + βar2
AM − PM(r) = αφr.2
1 + βφr2(1.4)
where r is the input signal amplitude and αa, βa, αφ and βφ are design parameters which characterise the
AM-AM and AM-PM functions respectively. For instance, Figure 1.5 plots a TWTA ampli�er functions using
parameters αa = 1.9638, βa = 0.9945, αφ = 2.5293 and βφ = 2.8168. IBO and OBO stand for backo�s and
are presented in the next section.
18 Chapter 1 - Digital communications over satellite channels
−20 −15 −10 −5 0 5 10−15
−10
−5
0
Input Normalised Power [dB]
Out
put P
ower
[dB
]IBO
OBO
Figure 1.5: AM-AM characteristic using Saleh's model with parameters αa = 1.9638 and βa = 0.9945
SSPA
A Solid State Power Ampli�er (SSPA) is a device that uses Field E�ect Transistors (FET) and thus relies on
solid components unlike a TWTA which uses a vacuum tube. A SSPA is composed of serial/parallel combi-
nations of FETs which used alone would have delivered limited gain. It usually consists of four stages using
power combiners, dividers and medium power ampli�ers. The power combiners are dissipative components
which leads to a lower energy e�ciency as their number increases.
In a similar fashion to TWTAs, SSPAs can be described by two functions namely AM-AM and AM-PM. An-
alytical models which can be used for representing these functions are di�erent from Saleh's equations (1.4).
In fact, two analytical models describing the SSPAs nonlinearity can be found in literature, the Rapp model
[Rapp, 1991] [Costa and Pupolin, 2002] and the Ghorbani model [Ghorbani and Sheikhan, 1991] respectively.
On the one hand, the Rapp's model de�nes AM-AM and AM-PM equation as follows:
AM −AM(r) = v r(1 +
(vrA0
)2p) 22p p > 0, A0 ≥ 0, v ≥ 0
AM − PM(r) = αΦ(vr
A0
)4(1.5)
where r is the input signal amplitude, v is called the small-signal gain, A0 is the saturation amplitude level
and p is a factor that controls the smoothness of the curve before saturation. In the AM-PM conversion, αΦ is
generally set to zero since the phase rotation is considered negligible for a SSPA compared to TWTA. On the
1.5 - Transponder modelling 19
−20 −15 −10 −5 0 5 100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Input normalised power [dB]
Pha
se [r
ad]
IBO
∆ φ
Figure 1.6: AM-PM characteristic using Saleh's model with parameters αφ = 2.5293 and βφ = 2.8168
other hand, Ghorbani's model presents a di�erent approximation of SSPA's AM-AM and AM-PM conversions.
These conversions write as:
AM −AM(r) = x1rx2
1 + x3rx2+ x4r
AM − PM(r) = y1ry2
1 + y3ry2+ y4r (1.6)
where r is the input signal amplitude, x1, x2, x3, x4 and y1, y2, y3, y4 are adjusting coe�cients. It can be
seen, that the Ghorbani model can be written as a Saleh decomposition for special values of the adjusting
parameters.
Comparison between TWTA and SSPA
For a comparison between the two classes of ampli�ers to be carried out, one needs to determine what is
the intended system use of these ampli�ers. Indeed, each of the TWTAs and SSPAs have advantages and
drawbacks, which implies they can only be assessed with regard to the application requirements. To do
so, authors in [Maral and Bousquet, 2002] present a set of comparative characteristics between TWTAs and
SSPAs which are presented in Table 1.4. On the one hand, SSPAs are lighter than TWTA but have less energy
e�ciency which makes them more suitable to small satellites in low orbits such as observation satellites. On
the other hand, TWTAs have better e�ciency and can operate over a wide range of frequencies which makes
them suitable for telecommunication applications such as broadcasting satellites. In the remaining of this
20 Chapter 1 - Digital communications over satellite channels
Characteristic TWTA SSPA
Operating band (GHz) C, Ku, Ka L,C
Saturated power output (W) 20− 250 20− 40Gain at saturation (dB) ∼ 55 70− 90Intermodulation product relative level (C/N)IM3 (dB) 10− 12 14− 18AM/PM conversion coe�cient Kp(/dB) 4.5 2
DC to RF e�ciency 50− 65 30− 45Mass including (kg) 1.5− 2.2 0.8− 1.5
Table 1.4: Comparative characteristics for TWTA and SSPA
−40 −30 −20 −10 0 10 20 30 40−60
−50
−40
−30
−20
−10
0
Frequency [Mhz]
Gai
n [d
B]
IMUXOMUX
Figure 1.7: Gain for IMUX and OMUX
thesis, the considered ampli�ers will be thus TWTAs, which will be modelled by Saleh's representation as in
(1.4).
1.5.2 Input and output multiplexers
The Input MUltipleXer (IMUX) is a band-pass �lter which aims at removing adjacent channels interference
caused by other input channels. The Output MUltipleXer (OMUX) consists of a band-pass �lter which rejects
the out-of-band radiation due to the spectral growth induced by the non linear ampli�er processing. The
reader is referred to Section 1.6.1 for more details about the impact of the ampli�cation on the power spectral
density. Figure 1.7 and Figure 1.8 illustrate the gain and group delay of typical 36MHz IMUX and OMUX
1.6 - Impact of system parameters on the non linear channel 21
−40 −30 −20 −10 0 10 20 30 40−5
0
5
10
15
20
25
30
35
40
Frequency [Mhz]
Gro
up d
elay
[ns]
IMUXOMUX
Figure 1.8: Group delay for IMUX and OMUX
�lters. The phase response is applied by integrating the group delay (GD) following:
φ(ω) =
∫GD(ω)dω (1.7)
where ω designates the frequency.
1.5.3 Saturation levels
In order to de�ne the operating point of a power ampli�er, it is useful to introduce two metrics which char-
acterise the back-o� towards the input saturation power and the output power respectively. We thus de�ne
the Input Back-O� (IBO) as the ratio between the input power Pin and the input saturation power Pin,sat as
follows:
IBO = −10 log10Pin
Pin,sat(1.8)
Similarly we de�ne the Output Back-O� (OBO) as the ratio between the output power Pout and the maximum
output power delivered by the PA as follows:
OBO = −10 log10Pout
Pout,sat(1.9)
Figure 1.5 and Figure 1.6 plot the TWTA transfer characteristics with its IBO and OBO operating points.
22 Chapter 1 - Digital communications over satellite channels
Figure 1.9: Satellite channel modelling
1.6 Impact of system parameters on the non linear channel
Let us consider the system depicted in Figure 1.9. A stream of symbols xn with a symbol duration Ts is pulse
shaped by a root raised cosine �lter with roll-o� α writing as:
h(t) =2α
π√Ts
cos[(1 + α)π tTs
]+
sin[(1−α)π tTs ]4α tTs
1−(
4α tTs
)2 (1.10)The resulting transmit signal is then sent to a satellite transponder where it is �rst �ltered with the IMUX,
ampli�ed by the HPA and then �ltered out by the OMUX. The output signal y(t) is broadcast to the receiving
station where an additive white Gaussian noise with variance σ2w. A matched receive �lter is used before
sampling at the corresponding Nyquist timing t0 + nTs. The resulting symbols zn depend on the system
parameters such as the root raised cosine roll-o�, the signalling rate and on the HPA back-o�, which hence
has an impact on the resulting system performance. It is thus interesting to investigate on the impact of each
of the aforementioned system parameters on the received symbols. To do so, we set the noise variance to zero
to assess only the non linear interference.
1.6.1 Impact of IBO
The IBO as de�ned in Section 1.5.3 is a key factor in the amount of ISI generated by the non linear satellite
channel. Figure 1.10 plots di�erent scatter-plots for a 16APSK using a root raised cosine of roll-o� α = 0.2
and for IBO = 0, 3, 6, 9dB. The �gure shows that the amount of ISI decreases with an increasing IBO which
is due to the linear-like behaviour of the HPA for very high back-o�s. It should be noted that the nonlinear
ISI is not isotropic, since there seems to be a correlation between real and imaginary parts of the ISI owing to
its elliptical shape. To illustrate this property, Figure 1.11 and Figure 1.12 plot the probability distribution
function of the power of ISI around the average constellation point, which is often called a centroid. It can
be seen that for low IBO values, the distribution of ISI of outer rings symbols is not a circular Gaussian
1.6 - Impact of system parameters on the non linear channel 23
−2 −1 0 1 2−2
−1
0
1
2
In−Phase
Qua
drat
ure
IBO = 0dB
−2 −1 0 1 2−2
−1
0
1
2
Qua
drat
ure
In−Phase
IBO = 3dB
−2 −1 0 1 2−2
−1
0
1
2
In−Phase
Qua
drat
ure
IBO = 6dB
−2 −1 0 1 2−2
−1
0
1
2
In−Phase
Qua
drat
ure
IBO = 9dB
Figure 1.10: Constellation for 16APSK with roll-o� α = 0.2
distribution, since its imaginary and real part histograms are not similar. Yet, with increasing IBO values, the
distribution of ISI becomes circular Gaussian which again is due to the linear operating region of the HPA for
high IBOs.
When being ampli�ed, the power spectral density of the signal is also modi�ed by the non linear processing.
The PSD is expanded leading to novel frequency components which is generally referred to as "spectral growth".
The amount of spectral growth depends on the IBO values and is depicted in Figure 1.13. It is clear that the
smaller the IBO, the larger the spectral growth, due to the increased nonlinearity of the power ampli�er.
1.6.2 Impact of the root raised cosine roll-o�
The root-raised cosine �lter introduces a memory in the satellite system which combined with the memoryless
non linear ampli�er leads to the observed ISI in Figure 1.10. One can wonder what is the impact of the roll-o�
24 Chapter 1 - Digital communications over satellite channels
−0.5 −0.4 −0.3 −0.2 −0.1 0 0.1 0.2 0.3 0.40
0.5
1
1.5
2
2.5
3
3.5
4
4.5
x
PD
F(x
)
Real part histogramReal part theoryImag part histogramImag part theory
Figure 1.11: PDF of real and imaginary parts of one outer ring centroid at IBO = 0dB
Symbol rate \ IBO 0dB -3dB -6dB -9dB27.5 Mbauds 0.0561 0.0440 0.0373 0.0326
30 Mbauds 0.0863 0.0695 0.0585 0.0552
32.5 Mbauds 0.1505 0.1282 0.1186 0.1081
Table 1.5: ISI variance for di�erent signal bandwidths
of the root raised cosine on the ISI power and shape. Figure 1.14 depicts the ISI variance for one of the outer
ring constellation symbols using di�erent IBOs and roll-o�s. The higher the roll-o�s, the lower the side lobes
of the impulse response are, and thus the less the impact of the non linearity. It can be further noticed, that
the dependence of the non linear interference power on the roll-o� decreases for large IBO values. Ultimately,
the roll-o� in�uence vanishes for very high IBO values, since the ampli�er consists then of a constant gain.
Thus, this would yield to interference-free received symbols, since the root-raised cosine �lters used in the
chain are Nyquist shapes.
1.6.3 Impact of the signal bandwidth in the presence of IMUX and OMUX
The IMUX and OMUX �lters present on both sides of the satellite non linear ampli�ers control the input and
output bandwidth of the satellite transponder signals. The multiplexing �lters de�ned in Section 1.5.2 were
designed for a 33MHz signal bandwidth, which for a certain roll-o� α leads to a desired symbol rate Rs =
33/(1 + α)Mbauds. For example with a roll-o� factor α = 0.2, the desired symbol rate is Rs = 27.5Mbauds.
1.7 - Non linear satellite channel models 25
−0.25 −0.2 −0.15 −0.1 −0.05 0 0.05 0.1 0.15 0.20
1
2
3
4
5
6
7
8
x
PD
F(x
)
Real part histogramReal part theoryImag part histogramImag part theory
Figure 1.12: PDF of real and imaginary part of one outer ring centroid at IBO = 9dB
If the symbol rate is higher than 27.5Mbauds, the �lters will be more frequency selective and thus will lead to
increased interference. In Table 1.5, the amount of ISI is expressed by means of the MSE between the received
symbols and their centroids and di�erent signal bandwidths are investigated. It can be seen that the larger
the symbol rate in comparison with the reference Rs = 27.5Mbauds, the higher the MSE.
1.7 Non linear satellite channel models
The issue of modelling the satellite transponder e�ects on the received demodulated signals has been investi-
gated in many previous studies. Indeed, modelling the satellite non linear channel is of primary importance in
order to adopt the adequate processing techniques in order to cope with adverse e�ects occurring in the satel-
lite link. Dependin